In the propsed study, we will examine the influence of visceral afferent components of the vagus nerve on hypothalamic neuroendocrine events related to reproduction. A role for the vagus nerve in these events was recently indicated by the observations that the estrous cycle and maintenance of pseudopregnancy were disrupted by abdominal vagotomy. The first group of studies proposed in the report will clarify the inhibitory effects of abdominal vagotomy on secretion of anterior pituitary hormones. In these studies, we will investigate the effects of abdominal vagotomy on: a) the induction of gonadotropin secretion by the "positive feedback of gonadal steroid hormones", b) release of gonadotropins after castration, and c) the nocturnal and diurnal prolactin surges of the pseudopregnant rat. A potential interaction of the function of the vagus nerve in satiety and the regulation of hormone secretion was suggested in a report indicating that prolactin is released afte eating in the human. We have proposed a study in this grant to determine if the vagus nerve effects the release of prolactin after feeding. We have also proposed determining whether chemical or electrical stimulation of the abdominal vagus nerve can either effect the release of anterior pituitary hormones, or alte pattens of hormone release. These studies should clarify the influence of the abdominal vagus nerve on the reproductive functions of the rat hypothalamus.